不能在一个简单的示例上使用JSTL [英] Can't use JSTL on a simple example

问题描述

这是我目前的情况: 我已经使用以下命令从Shell创建了一个Maven项目:

Here's my current situation: I've created a Maven project from my shell, using this command:

mvn archetype:generate -DgroupId=it.my.current.package.example -DartifactId=Example -DarchetypeArtifactId=maven-archetype-webapp -DinteractiveMode=false
mvn package

然后我打开Eclipse，将项目作为Maven导入.我将那些依赖项添加到我的 pom.xml

Then I opened Eclipse, imported the project as a Maven one. I added those dependencies to my pom.xml

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>3.1.0</version>
</dependency>
<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>jstl</artifactId>
    <version>1.2</version>
    <scope>provided</scope>
</dependency>

然后我创建了一个JSP和一个Servlet.

Then I created a JSP and a Servlet.

我的servlet仅设置了一些变量，而我的JSP将它们与一些JSTL一起使用.

My servlet just sets some variables and my JSP use them with some JSTL.

我在JSP上添加了以下标签:

I've added on my JSP this tag:

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>

JSP上的代码非常简单:

and the code on my JSP is really simple:

<c:forEach items="${requestScope.empList}" var="emp">
    <tr>
        <td><c:out value="${emp.id}"></c:out></td>
        <td><c:out value="${emp.name}"></c:out></td>
        <td><c:out value="${emp.role}"></c:out></td>
    </tr>
</c:forEach>

我的Servlet正在这样做:

My Servlet it's doing this:

List<Employee> empList = new ArrayList<Employee>();
Employee emp1 = new Employee();
emp1.setId(1); emp1.setName("Sam");emp1.setRole("Developer");
Employee emp2 = new Employee();
emp2.setId(2); emp2.setName("John");emp2.setRole("Manager");
empList.add(emp1);empList.add(emp2);
request.setAttribute("empList", empList);
RequestDispatcher rd = getServletContext().getRequestDispatcher("/home.jsp");
rd.forward(request, response);

Employee是一个简单的Bean.

Employee is a simple Bean.

当我尝试从Servlet运行此应用程序时，它实际上在我的JSP上向我显示了此信息:

When I try to run this application, from my Servlet, it actually shows me this, on my JSP:

${emp.id}      ${emp.name}      ${emp.role}

它并没有显示我在Servlet上设置的值.

And it's not showing the value that I set on my Servlet.

我是JSTL的新手，所以我首先用Google搜索了我的问题.我尝试在$TOMCAT_HOME/lib目录中添加jstl-1.2.jar，但是没有用.

I'm totally new to JSTL, so I googled first for my issue. I tried adding jstl-1.2.jar on my $TOMCAT_HOME/lib directory, but it didn't work.

那是什么问题?

要运行JSTL，我需要在容器和项目上进行哪些配置?我做的还不够吗?

what are the configuration I need to do on my container and project to run JSTL? Isn't enough what I've made?

推荐答案

我认为JSTL没问题.这种表示法:${emp.role}是EL(表达语言)，它不起作用.

I think that it is not a problem with JSTL. This notation: ${emp.role} is EL (Expression Language) and it is not working.

您没有在JSP文件中设置isELIgnored="true"吗?像这样:

Don't you have isELIgnored="true" set somewere in the JSP file? Like this:

<%@ page isELIgnored="true" %>

或者也许在web.xml中:

<el-ignored>true</el-ignored>

默认情况下应该为false，但是如果您使用的Servlet版本早于2.4，则默认值为true，因此在这种情况下，您需要在web.xml中将其设置为false:

It should be false by default, but if you use servlet version older than 2.4 then the default is true, so in that case you would need to set it to false in web.xml:

<jsp-config>
    <jsp-property-group>
        <url-pattern>*.jsp</url-pattern>
        <el-ignored>true</el-ignored>
    </jsp-property-group>
</jsp-config>

您在依赖项中具有版本3.1，但是在web.xml文件中使用了2.3版本.要使用Servlet 3.1，请尝试将web.xml更改为:

You have version 3.1 in dependencies, but in web.xml file 2.3 version is used. To use Servlet 3.1 try to change your web.xml into:

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">

    rest of the TAGs
</web-app>

也删除:

<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd">

(适用于2.3版本)

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